A huge asteroid will pass closer to Earth than the moon this week, but scientists say there is no chance of a collision.

Earth's close encounter with Asteroid 2005 YU55 will occur at 10:28am (AEDT) on Wednesday, as the space rock sails about 323,469 km from the planet.

"It is the first time since 1976 that an object of this size has passed this closely to the Earth," astronomer Scott Fisher, a program director with the National Science Foundation, said.

"It gives us a great and rare chance to study a near-Earth object like this."

The orbit and position of the asteroid, which is about 400 metres in diameter, is well known, added senior research scientist Don Yeomans from NASA's Jet Propulsion Laboratory in Pasadena, California.

"There is no chance that this object will collide with the Earth or moon," Mr Yeomans said.

Thousands of amateur and professional astronomers are expected to track YU55's approach, which will be visible from the northern hemisphere.

It will be too dim to be seen with the naked eye, however, and it will be moving too fast for viewing by the Hubble Space Telescope.

"The best time to observe it would be in the early evening on November 8 from the east coast of the United States," Mr Yeomans said.

"It is going to be very faint, even at its closest approach. You will need a decent-sized telescope to be able to actually see the object as it flies by."

Gravitational tugs

Scientists suspect YU55 has been visiting Earth for thousands of years, but because gravitational tugs from the planets occasionally tweak its path they cannot tell for sure how long the asteroid has been in its present orbit.

"These sorts of events have been happening for most of the lifetime of the Earth, about 4.5 billion years," Mr Fisher said.

Computer models showing the asteroid's path for the next 100 years show there is no chance it will hit Earth during that time, Mr Yeomans added.

"We do not think that it will ever impact the Earth or moon (but) we only have its orbit calculated for the next 100 years," he said.

Previous studies show the asteroid, which is blacker than charcoal, is what is called a C-type asteroid that is likely made of carbon-based materials and some silicate rock.

More information about its composition and structure are expected from radar images and chemical studies of its light as the asteroid passes Earth.

"I've read that we will be able to see details down to a size of about 4.5 metres across on the surface of the asteroid," Mr Fisher said.

NASA is working on a mission to return soil samples from an asteroid known as 1999 RQ36 in 2020 followed by a human mission to another asteroid in the mid-2020s.

There's people saying that there will be a tsunami drill that day, and a FEMA drill takeover of the media. They say to get your money out of the bank and get lots of water, food, etc. They report that NASA is telling its people to evacuate the coasts. Others say it will cause the Canary Islands volcano to landslide causing an additional monster tsunami in the Atlantic. Some think it may hit the continental US. It is part of the Mayan prophesy, the end of humanity, etc.The reality;400 meters across, will pass 200K miles away, visible if you are lucky, with a large binoculars or telescope, with probable moon interference with visual sightings.

Before every action and decision think of the consequences 7 generations into the future....Ute Rule of Life